1. Field of the Invention
The present invention relates to a host based printer for use in conjunction with a host computer, and more particularly to such a printer in which an error caused by fullness of a reception buffer is eliminated.
2. Description of the Related Art
Generally, printers receive code data from an external equipment and convert the code data to dot image data for printing. Because of a time needed for data conversion, there is a limit in increasing printing speed. Recently, host based printers have been extensively used. High performance personal computers are used as host computers which produce compressed dot image data and send the same to the host based printer.
The host based printer includes at least a transmission/reception circuit, a reception buffer, a DMA (direct memory access) controller, a decoding circuit, a line buffer, and a print controller. The transmission/reception circuit transmits data to the host computer and receives data therefrom. The reception buffer temporarily stores parallel compressed dot image data received from the host computer. The DMA controller, connected to both the transmission/reception circuit and the reception buffer, directly accesses the reception buffer to send the compressed dot image data stored therein to the decoding circuit. The decoding circuit decodes the compressed dot image data to reproduce the dot image data. The line buffer temporarily stores one raster line worth of dot image data and outputs serial data for supplying to a print driver. The host based printer is capable of performing a high speed decoding of the compressed dot image data to such an extent that the received compressed dot image data can be almost simultaneously printed.
The conventional host based printers will not start printing until a page end code is received. The page end code is representative of an end of the compressed image data on each page. Thereafter, each time when the page end code is received, the printers perform discharging of a printed sheet of paper and feeding a fresh sheet of paper through an interruption process. When the reception buffer becomes full before receipt of the page end code in a condition when printing has not yet been started, or when the reception buffer becomes full in a condition when printing has already been started, a print control is interrupted and an error process is executed during the interruption wherein an error message is displayed to indicate that the reception buffer has become full.
As described above, because the conventional host based printer does not start printing until one page worth of the image data is received at the reception buffer, the reception buffer is liable to become full before start of printing when a large amount of data is to be printed. Each time when the reception buffer becomes full before or after start of printing, an interruption process is executed to interrupt the print control and perform the error process during the interruption. Therefore, the print interruption occurs at a high frequency caused by fullness of the reception buffer and thus the print process is prosecuted with a low efficiency. Further problems exist such that the reception buffer with a small storage capacity is not available in the printer and the printer cannot draw customer's attraction because of frequently occuring error processes.